If it would ever happen again, could you take a picture of what your printhead looks like before you start taking it apart?
At the bottom of your nozzle, do you have this small teflon ring sealing of any openings?
It is weird that there is filament in the PTFE, but I can see how that could happen.
But on the spring?
Did it get on the spring when you took everything out and it got extra messy?
If your bowden tube is correctly in its place, how strongly is it secured?
Is there any movement in it at all or completely still?